The invention relates to a trip device of a molded case electrical circuit breaker having per pole a pair of contacts elastically urged into contact in the closed position of the circuit breaker and capable of separating due to the action of electrodynamic repulsion forces when the current flowing through the contacts exceeds a preset threshold to generate limitation of said current, said trip device having an overload and/or short-circuit fault detector which actuates an automatic opening operating mechanism of the circuit breaker on a fault.
A state-of-the-art trip device (U.S. Pat. No. 3,631,369) of the kind mentioned comprises a movable blade, arranged as a bimetal strip and subjected to the action of the electromagnetic trip device. An extension of the blade protrudes into the gas outflow duct of the arc extinguishing chamber. When breaking occurs the gas flow moves the blade to the tripping position. In most circuit breakers the gas outflow duct is located away from the trip device and the previously mentioned device is therefore not applicable. The blade is subjected to the polluting action of the gases and its correct operation is quickly hindered. Each pole must be equipped with a trip device of this kind and selectivity of tripping is not conceivable for the actuator reacting to the gas flow is integrated in the thermal and magnetic trip device.
The object of the present invention is to achieve a trip device providing both limitation and selectivity of tripping by simple, universal and reliable means.